As above, get $5 off for orders above $30. Shipping is $3.97 per book. I have compared a few books which I am interested in with Book Depository - and Betterworld's prices seem to work out to be about the same even after factoring in the shipping.
It's a great way to take advantage of the Paypal deal of $20 cashback with purchase over $50 as posted by Ozbargainer Nat. This $5 off sweetens the deal.
Enjoy!
ETA: Another code is "ptk0809" which gives you 10% discount. Thanks to Ozbargainer Hellfire. Remember to separate your purchase into 2 if above $100 since you will get two cashbacks from Paypal.
Does this really stack with the $20 cashback paypal offer?